The present invention relates to a motor driving circuit, and in particular, to a motor driving circuit for a single-phase and a three-phase motor in which the power consumption is reduced.
In a prior art motor driving circuit, for example, as disclosed in Japanese Patent Unexamined Publication Nos. 66864/80 and 66262/80, a PNP transistor and an NPN transistor are respectively connected to opposite ends of a motor driving coil, and electric power is supplied to the motor driving coil through the PNP transistor and the NPN transistor. In forming the motor driving circuit in an integrated circuit (IC), and in particular, in forming a portion of the driving circuit shown by a dotted line block A in FIG. 1 in the integrated circuit, there exists a barrier in that it has been difficult to realize a PNP transistor capable of operating in a considerably large current region due to an increase in chip size. For this reason, usually, as shown in FIG. 1, a relatively small-sized PNP transistor 3 and a large-sized NPN transistor 4 are used by connecting them in a Darlington connection. By virture of this Darlington connection, although the effect of an equivalent PNP transistor can be obtained, in the case of the transistor 4, the collector-emitter voltage V.sub.CE is required to be at least as large as the base-emitter voltage V.sub.BE (supposing that the collector-emitter voltage V.sub.CE of the transistor 3 is O V.) This fact causes a problem in that when motor coils 6 and 7 are driven, particularly, at low voltages, the efficiency .eta. of the motor (including loss in the driving circuit) is degraded to a great extent. Here, the efficiency .eta. of the motor is expressed by ##EQU1## output power being proportional to load torque.times.rotary speed. In this case, since the voltage in the above-mentioned formula is the collector-emitter voltage V.sub.CE of the transistor 4, by reducing the voltage V.sub.CE, the efficiency .eta. of the motor can be improved. In FIG. 1, reference numeral 1 designates a first power supply, 8 and 9 designate respectively input terminals for motor driving control signals for controlling the transistors 3, 4, and 5, and reference numeral 30 designates a second power supply.